Many homes and other buildings rely upon furnaces to provide heat during cool and/or cold weather. Typically, a furnace employs a burner that burns a fuel such as natural gas, propane, oil or the like, and provides heated combustion gases to the interior of a heat exchanger. The combustion gases typically proceed through the heat exchanger, are collected by a collector box, and then exhausted outside of the building via a vent or the like. In some cases, a combustion blower is provided to pull in combustion air into the burner, pull the combustion gases through the heat exchanger into the collector box, and push the combustion gases out the vent. At the same time, a circulating air blower typically forces return air from the building, and in some cases ventilation air from outside of the building, over or through the heat exchanger, thereby heating the air. The heated air is subsequently routed throughout the building via a duct system. A return duct system is typically employed to return air from the building to the furnace to be re-heated and then re-circulated.
In order to provide improved energy efficiency, some furnaces may be considered as having two or more stages, i.e., they can operate at two or more different burner firing rates, depending on how much heat is needed within the building. Some furnaces are known as modulating furnaces, because they can potentially operate at a number of different firing rates and/or across a range of firing rates. The firing rate of the furnace typically dictates the amount of gas and air that is required by the burner, as well as the heat that is produced by the burner.
To maintain energy efficiency across the various burner firing rates, the circulating air blower is sometimes regulated in accordance with burner firing rate to maintain a constant discharge air temperature, i.e., a constant temperature of the heated air being supplied to the building. When so regulated, the speed of the circulating air blower may be increased at higher firing rates and decreased at lower burner firing rates in order to maintain a constant discharge air temperature at the output of the furnace. While this can increase the overall energy efficiency of the furnace, relatively high circulating air blower speeds can negatively impact occupant comfort by creating a wind chill effect in the building, i.e., a feeling of draftiness caused by relatively high air flow in the building.